For effective utilization of a combustible gas, it is necessary to enrich the combustible gas to an appropriate extent by removing gas such as air from the source gas containing the combustible gas. There have been proposed a variety of apparatuses and methods for such enrichment of combustible gas. However, in the case of Patent Document 1 for example, as the source gas, there is employed a gas (so-called coal mine gas) generated from a coal mine that contains methane gas as the combustible gas. And, there is proposed an invention for enriching the methane gas for its utilization through separation of air (containing mainly, nitrogen, oxygen and carbon dioxide) from the source gas with using an adsorbent.
That is, in Patent Document 1, natural zeolite that has a very slow adsorption rate for methane gas as compared with nitrogen is employed as the adsorbent (in other words, there is employed an adsorbent which adsorbs nitrogen, oxygen and carbon dioxide with “priority” over the methane gas). And, there is proposed an invention relating to an apparatus and a method for enriching methane gas by the following technique. Namely, an amount of coal mine gas is introduced to a predetermined pressure into the adsorption tower charged with the adsorbent, with using a compressor or the like. In the course of this, oxygen, nitrogen and carbon dioxide contained in the coal mine gas are caused to be adsorbed first to a fore portion (lower portion) of the adsorption tower and methane gas having the lower adsorption rate is caused to be adsorbed to an aft portion (upper portion) of the adsorption tower. Further, this methane gas is released from the upper portion of the adsorption tower to the atmospheric pressure.
With the above, from the coal mine gas as source gas, methane gas is enriched by removal of the air with using the adsorbent. As a result, this enriched methane can be used as a fuel or the like.